Partially fluorinated benzene derivatives

ABSTRACT

Partially fluorinated benzene derivatives of the formula I ##STR1## in which R, A 1 , A 2 , Z 1 , Z 2 , L 1 , L 2  and m are as defined in claim 1, are suitable as components of liquid-crystalline media.

The invention relates to partially fluorinated benzene derivatives ofthe formula I ##STR2## where R is H, an alkyl or alkenyl radical having1 to 15 carbon atoms which is unsubstituted or monosubstituted by CN orCF₃ or at least monosubstituted by halogen, it also being possible forone or more CH₂ groups in these radicals to be replaced, in each caseindependently of one another, by --O--, --S--, ##STR3## --CO--,--CO--O--, --O--CO-- or --O--CO--O-- in such a manner that O atoms arenot linked directly to one another,

A¹ and A² are each, independently of one another, a

(a) trans-1,4-cyclohexylene radical in which, in addition, one or morenonadjacent CH₂ groups may be replaced by --O-- and/or --S--,

(b) 1,4-phenylene radical in which, in addition, one or two CH groupsmay be replaced by N,

(c) radical from the group consisting of 1,4-cyclohexenylene,1,4-bicyclo-(2,2,2)octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl,decahydronaphthalene-2,6-diyl and1,2,3,4-tetrahydronaphthalene-2,6-diyl,

it being possible for the radicals (a) and (b) to be substituted by oneor two fluorine atoms,

Z¹ and Z² are each, independently of one another, --CO--O--, --O--CO--,--CH₂ O--, --OCH₂ --, --CH₂ CH₂ --, --CH═CH--, --C≡C-- or a single bond,and one of the radicals Z¹ and Z² is alternatively --(CH₂)₄ -- or--CH═CH--CH₂ CH₂ --, and

m is 0, 1 or 2,

L¹ and L² are each, independently of one another, H or F.

The invention furthermore relates to the use of these compounds ascomponents of liquid-crystalline media, and to liquid-crystal andelectrooptical display elements which contain the liquid-crystallinemedia according to the invention.

The compounds of the formula I can be used as components ofliquid-crystalline media, in particular for displays based on theprinciple of the twisted cell, the guest-host effect, the effect ofdeformation of aligned phases or the effect of dynamic scattering.

The invention had the object of finding novel, stable liquid-crystallineor mesogenic compounds which are suitable as components ofliquid-crystalline media and in particular have at the same timecomparatively low viscosity and relatively high dielectric anisotropy.

It has now been found that compounds of the formula I are eminentlysuitable as components of liquid-crystalline media. In particular, theyhave comparatively low viscosities. They can be used to obtain stableliquid-crystalline media which have a broad mesophase range andadvantageous values for the optical and dielectric anisotropy. Thesemedia furthermore have very good low-temperature behavior.

The general formula in WO-00335 covers the novel compounds, but they arenot mentioned explicitly.

Similar fluorinated compounds are described in DE-A 41 01 600 and DE-A40 02 374.

In view of the extremely wide variety of areas of application of suchcompounds of high Δε, however, it was desirable to have furthercompounds of high nematogeneity available which have propertiesprecisely tailored to the particular application.

In addition, the provision of the compounds of the formula I verygenerally considerably broadens the range of liquid-crystallinesubstances which are suitable, from various applicational points ofview, for the preparation of liquid-crystalline mixtures.

The compounds of the formula I have a broad field of application.Depending on the choice of substituents, these compounds can be used asbase materials from which liquid-crystalline media are predominantlycomposed; however, it is also possible to add compounds of the formula Ito liquid-crystalline base materials from other classes of compound inorder, for example, to modify the dielectric and/or optical anisotropyof a dielectric of this type and/or to optimize its threshold voltageand/or viscosity.

In the pure state, the compounds of the formula I are colorless andformliquid-crystalline mesophases in a temperature range which isfavorably located for electrooptical use. They are stable chemically,thermally and to light.

The invention thus relates to the compounds of the formula I and to theuse of these compounds as components of liquid-crystalline media. Theinvention furthermore relates to liquid-crystalline media containing atleast one compound of the formula I, and to liquid-crystal displayelements, in particular electrooptical display elements, which containmedia of this type.

For reasons of simplicity below, A³ is a radical of the formula ##STR4##Y is CF₂ --CH₂ --CF₃, Cyc is a 1,4-cyclohexylene radical, Che is a1,4-cyclohexenylene radical, Dio is a 1,3-dioxane-2,5-diyl radical, Ditis a 1,3-dithiane-2,5-diyl radical, Phe is a 1,4-phenylene radical, Pydis a pyridine-2,5-diyl radical, Pyr is a pyrimidine-2,5-diyl radical andBi is a bicyclo(2,2,2)octylene radical, it being possible for Cyc and/orPhe to be unsubstituted or monosubstituted or disubstituted by F or CN.

A¹ and A² are preferably selected from the group consisting of Cyc, Che,Phe, Pyr, Pyd and Dio, it being preferred for only one of the radicalsA¹ and A² present in the molecule to be Che, Phe, Pyr, Pyd or Dio.

Accordingly, the compounds of the formula I cover bicyclic compounds ofthe subformulae Ia to Ib:

    R--A.sup.2 --A.sup.3 --Y                                   Ia

    R--A.sup.2 --Z.sup.2 --A.sup.3 --Y                         Ib

tricyclic compounds of the subformulae Ic to If:

    R--A.sup.1 --A.sup.2 --A.sup.3 --Y                         Ic

    R--A.sup.1 --Z.sup.1 --A.sup.2 --Z.sup.2 --A.sup.3 --Y     Id

    R--A.sup.1 --Z.sup.1 --A.sup.2 --A.sup.3 --Y               Ie

    R--A.sup.1 --A.sup.2 --Z.sup.2 --A.sup.3 --Y               If

and tetracyclic compounds of the subformulae Ig to Im:

    R--A.sup.1 --A.sup.1 --A.sup.2 --A.sup.3 --Y               Ig

    R--A.sup.1 --Z.sup.1 --A.sup.1 --A.sup.2 --A.sup.3 --Y     Ih

    R--A.sup.1 --A.sup.1 --Z.sup.1 --A.sup.2 --A.sup.3 --Y     Ii

    R--A.sup.1 --A.sup.1 --A.sup.2 --Z.sup.2 --A.sup.3 --Y     Ij

    R--A.sup.1 --Z.sup.1 --A.sup.1 --Z.sup.1 --A.sup.2 --A.sup.3 --YIk

    R--A.sup.1 --A.sup.1 --Z.sup.1 --A.sup.2 --Z.sup.2 --A.sup.3 --YIl

    R--A.sup.1 --Z.sup.1 --A.sup.1 --Z.sup.1 --A.sup.2 --Z.sup.2 --A.sup.3 --YIm

Of these, those of the subformulae Ia, Ib, Ic, Id, Ie, If, Ii and Il areparticularly preferred.

The preferred compounds of the subformula Ia are those of thesubformulae Iaa to Iaf:

    R--Phe--A.sup.3 --Y                                        Iaa

    R--Dio--A.sup.3 --Y                                        Iab

    R--Pyr--A.sup.3 --Y                                        Iac

    R--Pyd--A.sup.3 --Y                                        Iad

    R--Cyc--A.sup.3 --Y                                        Iae

    R--Che--A.sup.3 --Y                                        Iaf

Of these, those of the formulae Iaa and Iae are particularly preferred.

The preferred compounds of the subformula Ib are those of thesubformulae Iba to Ibc:

    R--Cyc--CH.sub.2 CH.sub.2 --A.sup.3 --Y                    Iba

    R--Cyc--COO --A.sup.3 --Y                                  Ibb

    R--Phe--COO--A.sup.3 --Y                                   Ibc

The preferred compounds of the subformula Ic are those of thesubformulae Ica to Icn:

    R--Phe--Phe--A.sup.3 --Y                                   Ica

    R--Phe--Pyd--A.sup.3 --Y                                   Icb

    R--Phe--Dio--A.sup.3 --Y                                   Icc

    R--Cyc--Cyc--A.sup.3 --Y                                   Icd

    R--Phe--Cyc--A.sup.3 --Y                                   Ice

    R--Cyc--Pyd--A.sup.3 --Y                                   Icf

    R--Pyd--Phe--A.sup.3 --Y                                   Icg

    R--Pyr--Phe--A.sup.3 --Y                                   Ich

    R--Phe--Pyr--A.sup.3 --Y                                   Ici

    R--Cyc--Pyr--A.sup.3 --Y                                   Icj

    R--Cyc--Phe--A.sup.3 --Y                                   Ick

    R--Dio--Phe--A.sup.3 --Y                                   Icl

    R--Che--Phe--A.sup.3 --Y                                   Icm

    R--Phe--Che--A.sup.3 --Y                                   Icn

Of these, those of the formulae Ica, Icd, Ice and Ick are particularlypreferred.

The preferred compounds of the subformula Id are those of thesubformulae Ida to Idk:

    R--Phe--Z.sup.1 --Phe--Z.sup.2 --A.sup.3 --Y               Ida

    R--Phe--Z.sup.1 --Dio--Z.sup.2 --A.sup.3 --Y               Idb

    R--Cyc--Z.sup.1 --Cyc--Z.sup.2 --A.sup.3 --Y               Idc

    R--Cyc--Z.sup.1 --Pyr--Z.sup.2 --A.sup.3 --Y               Idd

    R--Pyd--Z.sup.1 --Phe--Z.sup.2 --A.sup.3 --Y               Ide

    R--Phe--Z.sup.1 --Pyd--Z.sup.2 --A.sup.3 --Y               Idf

    R--Pyr--Z.sup.1 --Phe--Z.sup.2 --A.sup.3 --Y               Idg

    R--Phe--Z.sup.1 --Pyr--Z.sup.2 --A.sup.3 --Y               Idh

    R--Phe--Z.sup.1 --Cyc--Z.sup.2 --A.sup.3 --Y               Idi

    R--Cyc--Z.sup.1 --Phe--Z.sup.2 --A.sup.3 --Y               Idj

    R--Dio--Z.sup.1 --Phe--Z.sup.2 --A.sup.3 --Y               Idk

The preferred compounds of the subformula Ie are those of thesubformulae Iea to Iej:

    R--Pyr--Z.sup.1 --Phe--A.sup.3 --Y                         Iea

    R--Dio--Z.sup.1 --Phe--A.sup.3 --Y                         Ieb

    R--Phe--Z.sup.1 --Phe--A.sup.3 --Y                         Iec

    R--Cyc--Z.sup.1 --Phe--A.sup.3 --Y                         Ied

    R--Phe--Z.sup.1 --Cyc--A.sup.3 --Y                         Iee

    R--Cyc--Z.sup.1 --Cyc--A.sup.3 --Y                         Ief

    R--Phe--Z.sup.1 --Dio--A.sup.3 --Y                         Ieg

    R--Pyd--Z.sup.1 --Phe--A.sup.3 --Y                         Ieh

    R--Phe--Z.sup.1 --Pyr--A.sup.3 --Y                         Iei

    R--Cyc--Z.sup.1 --Pyr--A.sup.3 --Y                         Iej

The preferred compounds of the subformula If are those of thesubformulae Ifa to Ifn

    R--Pyr--Phe--Z.sup.2 --A.sup.3 --Y                         Ifa

    R--Pyr--Phe--OCH.sub.2 --A.sup.3 --Y                       Ifb

    R--Phe--Phe--Z.sup.2 --A.sup.3 --Y                         Ifc

    R--Phe--Phe--OOC--A.sup.3 --Y                              Ifd

    R--Cyc--Cyc--Z.sup.2 --A.sup.3 --Y                         Ife

    R--Cyc--Cyc--CH.sub.2 CH.sub.2 --A.sup.3 --Y               Iff

    R--Pyd--Phe--Z.sup.2 --A.sup.3 --Y                         Ifg

    R--Dio--Phe--Z.sup.2 --A.sup.3 --Y                         Ifh

    R--Phe--Cyc--Z.sup.2 --A.sup.3 --Y                         Ifi

    R--Phe--Pyd--Z.sup.2 --A.sup.3 --Y                         Ifj

    R--Che--Phe--Z.sup.2 --A.sup.3 --Y                         Ifk

    R--Phe--Che--Z.sup.2 --A.sup.3 --Y                         Ifl

    R--Cyc--Phe--Z.sup.2 --A.sup.3 --Y                         Ifm

    R--Cyc--Phe--OOC--A.sup.3 --Y                              Ifn

Preference is also given to compounds of the formula I and allsubformulae in which A¹ and A² are 1,4-phenylene which ismonosubstituted or disubstituted by F or monosubstituted by CN. Theseare, in particular, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene and3,5-difluoro-1,4-phenylene, and 2-cyano-1,4-phenylene and3-cyano-1,4-phenylene. In a particularly preferred embodiment, A² is3,5-difluoro-1,4-phenylene, and m is 1 or 2.

A³ is preferably ##STR5##

Z¹ and Z² are preferably a single bond, --CO--O--, --O--CO-- and --CH₂CH₂ --, and secondarily preferably --CH₂ O-- and --OCH₂ --.

If one of the radicals Z¹ and Z² is --(CH₂)₄ -- or --CH═CH--CH₂ CH₂ --,the other radical Z¹ or Z² (if present) is preferably a single bond.

Preferred compounds of this type conform to the subformula I' ##STR6##in which Z² is --(CH₂)₄ -- or --CH═CH--CH₂ CH₂ --, and R, A¹, A², L¹, L²and m are as defined under formula I. The preferred meanings for R, A¹,A² and m also correspond to those for the compounds of the formula I.

m is preferably 1 or 0, particularly preferably 1.

If R is an alkyl radical and/or an alkoxy radical, this may bestraight-chain or branched. It is preferably straight-chain, has 2, 3,4, 5, 6 or 7 carbon atoms and is accordingly preferably ethyl, propyl,butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxyor heptoxy, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, nonoxy, decoxy,undecoxy, dodecoxy, tridecoxy or tetradecoxy.

Oxaalkyl is preferably straight-chain 2-oxapropyl (=methoxymethyl),2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3- or4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl,2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonylor 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

If R is an alkyl radical in which one CH₂ group has been replaced by--CH═CH--, this may be straight-chain or branched. It is preferablystraight-chain and has 2 to 10 carbon atoms. It is accordinglyparticularly vinyl, prop-1- or prop-2-enyl, but-1-, 2- or but-3-enyl,pent-1-, 2-, 3- or pent-4-enyl, hex-1-, 2-, 3-, 4- or hex-5-enyl,hept-1-, 2-, 3-, 4-, 5- or hept-6-enyl, oct-1-, 2-, 3-, 4-, 5-, 6- oroct-7-enyl, non-1-, 2-, 3-, 4-, 5-, 6-, 7-or non-8-enyl, or dec-1-, 2-,3-, 4-, 5-, 6-, 7-, 8- or dec-9-enyl.

If R is an alkyl radical in which one CH₂ group has been replaced by--O-- and one has been replaced by --CO--, these are preferablyadjacent. These thus contain an acyloxy group --CO--O-- or anoxycarbonyl group --O--CO--. These are preferably straight-chain andhave 2 to 6 carbon atoms.

They are accordingly particularly acetyloxy, propionyloxy, butyryloxy,pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl,butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl,2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetyloxypropyl,3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl,.methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl,butoxycarbonylmethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl,3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl)butyl.

If R is an alkyl radical in which one CH₂ group has been replaced byunsubstituted or substituted --CH═CH-- and an adjacent CH₂ group hasbeen replaced by CO or CO--O or O--CO--, this may be straight-chain orbranched. It is preferably straight-chain and has 4 to 13 carbon atoms.It is accordingly particularly acryloyloxymethyl, 2-acryloyloxyethyl,3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl,6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl,9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl,2-methacryloyloxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxybutyl,5-methacryloyloxypentyl, 6-methacryloyloxyhexyl,7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl or9-methacryloyloxynonyl.

If R is an alkyl or alkenyl radical which is monosubstituted by CN orCF₃, this radical is preferably straight-chain and the substitution isby CN or CF₃ in the ω-position.

If R is an alkyl or alkenyl radical which is at least monosubstituted byhalogen, this radical is preferably straight-chain and halogen ispreferably F or Cl. In the case of multiple substitution, halogen ispreferably F. The resulting radicals also include perfluorinatedradicals. In the case of monosubstitution, the fluorine or chlorinesubstituent can be in any desired position, but is preferably in theω-position.

Compounds of the formula I which contain wing groups R which aresuitable for polymerization reactions are suitable for the preparationof liquid-crystalline polymers.

Compounds of the formula I containing branched wing groups R mayoccasionally be of importance due to better solubility in customaryliquid-crystalline base materials, but in particular as chiral dopes ifthey are optically active. Smectic compounds of this type are suitableas components for ferroelectric materials.

Compounds of the formula I having S_(A) phases are suitable, forexample, for thermally addressed displays.

Branched groups of this type generally contain not more than one chainbranch. Preferred branched radicals R are isopropyl, 2-butyl(=1-methylpropyl), isobutyl (=2 -methylpropyl), 2-methylbutyl, isopentyl(=3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl,2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy,3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy,1-methylhexoxy and 1-methylheptoxy.

If R is an alkyl radical in which two or more CH₂ groups have beenreplaced by --O-- and/or --CO--O--, this may be straight-chain orbranched. It is preferably branched and has 3 to 12 carbon atoms. It isaccordingly particularly biscarboxymethyl, 2,2-biscarboxyethyl,3,3-biscarboxypropyl, 4,4-biscarboxybutyl, 5,5-biscarboxypentyl,6,6-biscarboxyhexyl, 7,7-biscarboxyheptyl, 8,8-biscarboxyoctyl,9,9-biscarboxynonyl, 10,10-biscarboxydecyl, bis(methoxycarbonyl)methyl,2,2-bis(methoxycarbonyl)ethyl, 3,3-bis(methoxycarbonyl)propyl,4,4-bis(methoxycarbonyl)butyl, 5,5-bis(methoxycarbonyl)pentyl, 6,6-bis(methoxycarbonyl)hexyl, 7,7-bis(methoxycarbonyl)heptyl,8,8-bis(methoxycarbonyl)octyl, bis(ethoxycarbonyl) methyl,2,2-bis(ethoxycarbonyl)ethyl, 3,3-bis(ethoxycarbonyl) propyl,4,4-bis(ethoxycarbonyl)butyl or 5,5-bis(ethoxycarbonyl)hexyl.

Compounds of the formula I which contain wing groups R which aresuitable for polycondensations are suitable for the preparation ofliquid-crystalline polycondensates.

Formula I covers the racemates of these compounds and the opticalantipodes, and mixtures thereof.

Of these compounds of the formula I and the subformulae, those arepreferred in which at least one of the radicals present therein has oneof the preferred meanings indicated.

In the compounds of the formula I, those stereoisomers in which therings Cyc and piperidine are trans-1,4-disubstituted are preferred.Those of the abovementioned formulae which contain one or more groupsPyd, Pyr and/or Dio in each case cover the two 2,5-positional isomers.

Preferred smaller groups of compounds are those of the subformulae I1 toI30: ##STR7##

Particular preference is given to compounds of the formulae I1, I3, I6,I9, I12 and I25.

The 1,4-cyclohexenylene group preferably has the following structures:##STR8##

The compounds of the formula I are prepared by methods known per se, asdescribed in the literature (for example in the standard works, such asHouben-Weyl, Methoden der Organischen Chemie (Methods of OrganicChemistry), Georg-Thieme-Verlag, Stuttgart), to be precise underreaction conditions which are known and suitable for said reactions.

Use may also be made here of variants which are known per se, but arenot described here in greater detail.

The compounds of the formula I can be prepared from the correspondingketones, obtainable by Friedel-Crafts acylation of the compounds of theformula II. The ketone is first converted into the correspondingthioketal and subsequently reacted with a brominating agent, for example1,3-dibromo-5,5-dimethylhydantoin (NDBDH) or N-bromosuccinimide (NBS),and a fluorinating agent, such as, for example, pyridinium fluoride,tetrabutylammonium fluoride, diethylaminosulfur trifluoride (DAST) orcesium fluoride. ##STR9##

The compounds of the formula I can furthermore be prepared as follows:##STR10##

The compounds of the formula I are furthermore obtainable from thetrifluoropropynebenzene derivatives, which are disclosed in EP 0 480217. ##STR11##

The compounds of the formula II can be prepared, for example, inaccordance with the following synthesis scheme: ##STR12##

The starting materials are either known or can be prepared analogouslyto known compounds.

Esters of the formula I can also be obtained by esterification ofcorresponding carboxylic acids (or reactive derivatives thereof) usingalcohols or phenols (or reactive derivatives thereof) or by the DCCmethod (DCC=dicyclohexylcarbodiimide).

The corresponding carboxylic acids and alcohols or phenols are known orcan be prepared analogously to known methods.

In a further process for the preparation of the compounds of the formulaI, an aryl halide is reacted with an olefin in the presence of atertiary amine and in the presence of a palladium catalyst (cf. R. F.Heck, Acc. Chem. Res. 12 (1979) 146). Examples of suitable aryl halidesare chlorides, bromides and iodides, in particular bromides and iodides.The tertiary amines necessary for the success of the coupling reaction,such as, for example, triethylamine, are also suitable as solvent.Examples of suitable palladium catalysts are palladium salts, inparticular Pd(II) acetate, with organic phosphorus (III) compounds, suchas, for example, triarylphosphines. This reaction can be carried out inthe presence or absence of an inert solvent at temperatures betweenabout 0° and 150° preferably between 20° and 100°; examples of suitablesolvents are nitriles, such as acetonitrile, or hydrocarbons, such asbenzene or toluene. The aryl halides and olefins employed as startingmaterials are frequently commercially available or can be prepared byprocesses known from the literature, for example by halogenation ofcorresponding parent compounds or by elimination reactions oncorresponding alcohols or halides.

In this way, it is possible to prepare, for example, stilbenederivatives. The stilbenes can furthermore be prepared by reacting a4-substituted benzaldehyde with a corresponding phosphorus ylide by theWitrig method. However, it is also possible to prepare tolans of theformula I by employing monosubstituted acetylene in place of the olefin(Synthesis 627 (1980) or Tetrahedron Lett. 27, 1171 (1986)).

A further way of coupling aromatic compounds is to react aryl halideswith aryl tin compounds. These reactions are preferably carried out withaddition of a catalyst, such as, for example, a palladium(O) complex, ininert solvents, such as hydrocarbons, at high temperatures, for examplein boiling xylene, under a protective gas.

Coupling reactions of alkynyl compounds with aryl halides can be carriedout analogously to the process described by A. O. King, E. Negishi, F.J. Villani and A. Silveira in J. Org. Chem. 43, 358 (1978).

Tolans of the formula I can also be prepared via theFritsch-Buttenberg-Wiechell rearrangement (Ann. 279, 319, 1984), inwhich 1,1-diaryl-2-haloethylenes are rearranged in the presence ofstrong bases to give diaryl acetylenes.

Tolans of the formula I can also be prepared by brominating thecorresponding stilbenes followed by dehydrohalogenation. Use can also bemade here of variants of these reactions known per se, which are notdescribed here in greater detail.

Ethers of the formula I can be obtained by etherification ofcorresponding hydroxyl compounds, preferably corresponding phenols, thehydroxyl compound expediently first being converted into a correspondingmetal derivative, for example into the corresponding alkali metalalkoxide or alkali metal phenoxide by treatment with NaH, NaNH₂, NaOH,KOH, Na₂ CO₃ or K₂ CO₃. This metal derivative can then be reacted withthe appropriate alkyl halide, sulfonate or dialkyl sulfate, expedientlyin an inert solvent, such as, for example, acetone, 1,2-dimethoxyethane,DMF or dimethyl sulfoxide, or alternatively with an excess of aqueous oraqueous-alcoholic NaOH or KOH at temperatures between about 20° and 100°C.

The starting materials are either known or can be prepared analogouslyto known compounds.

The compounds of the formula I' in which Z² =--(CH₂)₄ -- can be preparedin accordance with the following scheme: ##STR13##

The Pd(II)-catalyzed coupling reaction either gives the target productI' directly or a precursor, into which the radical --Y is introducedentirely analogously to the above methods for compounds of the formulaI.

The compounds of the formula I' in which Z² =--CH═CH--CH₂ CH₂ -- can beprepared by the Witrig method as shown in the following scheme:##STR14##

The preferred trans-isomers can be prepared by isomerization methodsknown from the literature. The precursors where R⁰ =H which may beobtained are converted into the compounds of the formula I' entirelyanalogously to the precursors of the compounds of the formula I byintroduction of the radical --Y--.

The aldehydes can be obtained by Heck reaction of appropriatelysubstituted 1-bromo-3-fluorobenzene derivatives with allyl alcohol.

The synthesis of some particularly preferred compounds is shown below ingreater detail: ##STR15##

The liquid-crystalline media according to the invention preferablycontain 2 to 40, in particular 4 to 30, components as furtherconstituents besides one or more compounds according to the invention.These media very particularly preferably contain 7 to 25 componentsbesides one or more compounds according to the invention. These furtherconstituents are preferably selected from nematic or nematogenic(monotropic or isotropic) substances, in particular substances from theclasses of the azoxybenzenes, benzylidene anilines, biphenyls,terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl estersof cyclohexanecarboxylic acid, phenyl or cyclohexyl esters ofcyclohexylbenzoic acid, phenyl or cyclohexyl esters ofcyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters of benzoicacid, of cyclohexanecarboxylic acid and ofcyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes,cyclohexylbiphenyls, phenylcyclohexylcyclohexanes,cyclohexylcyclohexanes, cyclohexylcyclohexylcyclohexenes,1,4-bis-cyclohexylbenzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl- orcyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenylorcyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes,1,2-diphenylethanes, 1,2-dicyclohexylethanes,1-phenyl-2-cyclohexylethanes,1-cyclohexyl-2-(4-phenylcyclohexyl)ethanes,1-cyclohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexylphenylethanes,optionally halogenated stilbenes, benzyl phenyl ethers, tolans andsubstituted cinnamic acids. The 1,4-phenylene groups in these compoundsmay also be fluorinated.

The most important compounds suitable as further constituents of mediaaccording to the invention can be characterized by the formulae 1, 2, 3,4 and 5:

    R'--L--E--R"                                               1

    R'--L--COO--E--R"                                          2

    R'--L--OOC--E--R"                                          3

    R'--L--CH.sub.2 CH.sub.2 --E--R"                           4

    R'--L--C≡C--E--R"                                    5

In the formulae 1, 2, 3, 4 and 5, L and E, which may be identical ordifferent, are in each case, independently of one another, a bivalentradical from the group formed by --Phe--, --Cyc--, --Phe--Phe--,--Phe--Cyc--, --Cyc--Cyc--, --Pyr--, --Dio--, --G--Phe-- and --G--Cyc--and their mirror images, where Phe is unsubstituted orfluorine-substituted 1,4-phenylene, Cyc is trans-1,4-cyclohexylene or1,4-cyclohexylene, Pyr is pyrimidine-2,5-diyl or pyridine-2,5-diyl, Diois 1,3-dioxane-2,5-diyl and G is 2-(trans-1,4-cyclohexyl)ethyl,pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.

One of the radicals L and E is preferably Cyc, Phe or Pyr. E ispreferably Cyc, Phe or Phe-Cyc. The media according to the inventionpreferably contain one or more components selected from the compounds ofthe formulae 1, 2, 3, 4 and 5 in which L and E are selected from thegroup cosisting of Cyc, Phe and Pyr and simultaneously one or morecomponents selected from the compounds of the formulae 1, 2, 3, 4 and 5in which one of the radicals L and E is selected from the groupconsisting of Cyc, Phe and Pyr and the other radical is selected fromthe group consisting of --Phe--Phe--, --Phe--Cyc--, --Cyc--Cyc--,--G--Phe-- and --G--Cyc--, and optionally one or more componentsselected from the compounds of the formulae 1, 2, 3, 4 and 5 in whichthe radicals L and E are selected from the group consisting of--Phe--Cyc--, --Cyc--Cyc--, --G--Phe-- and --G--Cyc--.

In a smaller subgroup of compounds of formulae 1, 2, 3, 4 and 5 R' andR" are, in each case independently of one another, alkyl, alkenyl,alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8 carbonatoms. This smaller subgroup is referred to as group A below, and thecompounds are labeled with the subformulae 1a, 2a, 3a, 4a and 5a. Inmost of these compounds, R' and R" are different from one another, oneof these radicals usually being alkyl, alkenyl, alkoxy or alkoxyalkyl.

In another smaller subgroup of the compounds of the formulae 1, 2, 3, 4and 5, known as group B, R" is --F, --Cl, --NCS or --(O)_(i) CH₃₋(k+1)F_(k) Cl₁, where i is 0 or 1 and k+1 is 1, 2 or 3; the compounds inwhich R" has this meaning are labeled with the subformulae 1b, 2b, 3b,4b and 5b. Particular preference is given to the compounds of thesubformulae 1b, 2b, 3b, 4b and 5b in which R" is --F, --Cl, --NCS,--CF₃, --OCHF₂ or --OCF₃.

In the compounds of the subformulae 1b, 2b, 3b, 4b and 5b, R' is asdefined for the compounds of the subformulae 1a-5a and is preferablyalkyl, alkenyl, alkoxy or alkoxyalkyl.

In a further smaller subgroup of the compounds of the formulae 1, 2, 3,4 and 5, R" is --CN; this subgroup is known as group C below, and thecompounds of this subgroup are accordingly described by subformulae 1c,2c, 3c, 4c and 5c. In the compounds of the subformulae 1c, 2c, 3c, 4cand 5c, R' is as defined for the compounds of the subformulae 1a-5a andis preferably alkyl, alkoxy or alkenyl.

In addition to the preferred compounds of groups A, B and C, othercompounds of the formulae 1, 2, 3, 4 and 5 with other variants of theproposed substituents are also common. All these substances can beobtained by methods known from the literature or analogously thereto.

The media according to the invention preferably contain one or morecompounds selected from group A and/or group B and/or group C inaddition to compounds of the formula I according to the invention. Theproportions by weight of the compounds from these groups in the mediaaccording to the invention are preferably

Group A: from 0 to 90%, preferably 20 to 90%, in particular from 30 to90%

Group B: from 0 to 80%, preferably from 10 to 80%, in particular from 10to 65%

Group C: from 0 to 80%, preferably from 5 to 80%, in particular from 5to 50%

the sum of the proportions by weight of the compounds from groups Aand/or B and/or C present in the respective media according to theinvention preferably being 5-90% and in particular 10-90%.

The media according to the invention preferably contain 1 to 40%, inparticular preferably 5 to 30%, of compounds according to the invention.Further preferred media are those which contain more than 40%, inparticular 45 to 90%, of compounds according to the invention. The mediapreferably contain three, four or five compounds according to theinvention.

The media according to the invention are prepared in a manner which iscustomary per se. In general, the components are dissolved in oneanother, expediently at elevated temperature. By means of suitableadditives, the liquid-crystalline phases can be modified in accordancewith the invention in a manner such that they can be used in all typesof liquid-crystal display elements which have hitherto been disclosed.Additives of this type are known to those skilled in the art and aredescribed in detail in the literature (H. Kelker/R. Hatz, Handbook ofLiquid Crystals, Verlag Chemie, Weinheim, 1980). For example, pleochroicdyes can be added for the production of colored guest-host systems, orsubstances can be added to modify the dielectric anisotropy, theviscosity and/or the orientation of the nematic phases.

In the present application and in the examples below, the structures ofthe liquid-crystal compounds are indicated by means of acronyms, thetransformation into chemical formulae being carried out in accordancewith tables A and B below. All radicals C_(n) H_(2n+1) and C_(m)H_(2m+1) are straight-chain alkyl radicals having n or m carbon atomsrespectively. The coding in table B is self-evident. In table A, onlythe acronym for the parent structure is shown. In individual cases, theacronym for the parent structure is followed, separated by a hyphen, bya code for the substituents R¹, R², L¹ and L² :

    __________________________________________________________________________    Code for R.sup.1,                                                             R.sup.2, L.sup.1, L.sup.2                                                             R.sup.1         R.sup.2  L.sup.1                                                                          L.sup.2                                   __________________________________________________________________________    nm      C.sub.n H.sub.2n+1                                                                            C.sub.m H.sub.2m+1                                                                     H  H                                         nOm     C.sub.n H.sub.2n+1                                                                            OC.sub.m H.sub.2m+1                                                                    H  H                                         nO.m    OC.sub.n H.sub.2n+1                                                                           C.sub.m H.sub.2m+1                                                                     H  H                                         n       C.sub.n H.sub.2n+1                                                                            CN       H  H                                         nN.F    C.sub.n H.sub.2n+1                                                                            CN       H  F                                         nF      C.sub.n H.sub.2n+1                                                                            F        H  H                                         nOF     OC.sub.n H.sub.2n+1                                                                           F        H  H                                         nCl     C.sub.n H.sub.2n+1                                                                            Cl       H  H                                         nF.F    C.sub.n H.sub.2n+1                                                                            F        H  F                                         nF.F.F  C.sub.n H.sub.2n+1                                                                            F        F  F                                         nCF.sub.3                                                                             C.sub.n H.sub.2n+1                                                                            CF.sub.3 H  H                                         nOCF.sub.3                                                                            C.sub.n H.sub.2n+1                                                                            OCF.sub.3                                                                              H  H                                         nOCF.sub.2                                                                            C.sub.n H.sub.2n+1                                                                            OCHF.sub.2                                                                             H  H                                         nS      C.sub.n H.sub.2n+1                                                                            NCS      H  H                                         rVsN    C.sub.r H.sub.2r+1 --CH═CH--C.sub.s H.sub.2s --                                           CN       H  H                                         rEsN    C.sub.r H.sub.2r+1 --O--C.sub.s H.sub.2s --                                                   CN       H  H                                         nAm     C.sub.n H.sub.2n+1                                                                            COOC.sub.m H.sub.2m+1                                                                  H  H                                         __________________________________________________________________________

                                      TABLE A                                     __________________________________________________________________________     ##STR16##                                                                                                    ##STR17##                                      ##STR18##                                                                                                    ##STR19##                                      ##STR20##                                                                                                    ##STR21##                                      ##STR22##                                                                                                    ##STR23##                                      ##STR24##                                                                                                    ##STR25##                                      ##STR26##                                                                                                    ##STR27##                                      ##STR28##                                                                                                    ##STR29##                                      ##STR30##                                                                                                    ##STR31##                                      ##STR32##                                                                                                    ##STR33##                                      ##STR34##                                                                                                    ##STR35##                                      ##STR36##                                                                    __________________________________________________________________________

                                      TABLE B                                     __________________________________________________________________________     ##STR37##                                                                                                  ##STR38##                                        ##STR39##                                                                                                  ##STR40##                                        ##STR41##                                                                                                  ##STR42##                                        ##STR43##                                                                                                  ##STR44##                                        ##STR45##                                                                                                  ##STR46##                                        ##STR47##                                                                     ##STR48##                                                                                                  ##STR49##                                        ##STR50##                                                                                                  ##STR51##                                        ##STR52##                                                                                                  ##STR53##                                        ##STR54##                                                                     ##STR55##                                                                                                  ##STR56##                                        ##STR57##                                                                                                  ##STR58##                                        ##STR59##                                                                                                  ##STR60##                                        ##STR61##                                                                                                  ##STR62##                                        ##STR63##                                                                                                  ##STR64##                                        ##STR65##                                                                                                  ##STR66##                                       __________________________________________________________________________

The examples below are intended to illustrate the invention withoutrepresenting a limitation. Above and below, percentages are by weight.All temperatures are given in degrees celcius. m.p. denotes meltingpoint, c.p.=clearing point. Furthermore, C=crystalline state, N=nematicphase, S=smectic phase, I=isotropic phase. The numbers between thesesymbols indicate the transition temperatures. An denotes opticalanisotropy (589 nm, 20° C.) and the viscosity (mm² /sec) was determinedat 20° C.

"Conventional work-up" means that water is added if desired, the mixtureis extracted with dichloromethane, diethyl ether or toluene, the organicphase is separated, dried and evaporated, and the product is purified bydistillation under reduced pressure or crystallization and/orchromatography. The following abbreviations are used:

    ______________________________________                                        DAST          Diethylaminosulfur trifluoride                                  DMEU          1,3-Dimethyl-2-imidazoladinone                                  POT           Potassium tert-butoxide                                         THP           Tetrahydrofuran                                                 pTSOH         P-Toluenesulfonic acid                                          ______________________________________                                    

EXAMPLE 1 ##STR67## STEP 1.1 ##STR68##

11.5 g of ethyl para-bromophenylmalonate, dissolved in 20 ml ofdichloromethane, are weighed into a nickel Monell autoclave and cooledto -70° C., and 18 g of anhydrous hydrofluoric acid are added. Afterthawing at room temperature, the mixture is stirred for 2 hours and thencooled to -196° C., and 20 g of sulfur tetrafluoride are condensed in.The autoclave is warmed to 60° C. and left at this temperature for 2hours. After the mixture has been cooled to room temperature, thevolatile constituents are removed by distillation, the autoclave isopened, and the contents are taken up in dichloromethane. Afterneutralization by means of bicarbonate solution and drying overmagnesium sulfate, the mixture is evaporated and distilled in vacuo.

STEP 1.2 ##STR69##

6.2 mmol of p-trans-[4-propylcyclohexyl]phenylboronic acid and 75 ml oftoluene are added to 0.025 mol of NaOH and 7.5 ml of H₂ O. The mixtureis stirred at 40° C. for 15 minutes, and 6.2 mmol ofp-bromo-1,1,3,3,3-pentafluoropropylbenzene and 0.14 g oftetrakistriphenylphosphinepalladium(0) are added. The mixture issubsequently heated to 100° C., refluxed for 16 hours and then allowedto cool to room temperature, and the organic phase is separated off,mixed with water and subjected to customary work-up.

The following compounds of the formula ##STR70## are preparedanalogously:

    __________________________________________________________________________    R        (A.sup.1Z.sup.1).sub.mA.sup.2Z.sup.2                                                             L.sup.1                                                                          L.sup.2                                        __________________________________________________________________________    C.sub.2 H.sub.5                                                                         ##STR71##         H  H                                              C.sub.2 H.sub.5                                                                         ##STR72##         H  F                                              C.sub.2 H.sub.5                                                                         ##STR73##         F  F                                              n-C.sub.3 H.sub.7                                                                       ##STR74##         H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR75##         F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR76##         H  H C 86 S.sub.B 113 I Δn = +0.133;                                       Δε = 10.67                       n-C.sub.5 H.sub.11                                                                      ##STR77##         H  F                                              n-C.sub.5 H.sub.11                                                                      ##STR78##         F  F                                              n-C.sub.6 H.sub.13                                                                      ##STR79##         H  H                                              n-C.sub.6 H.sub.13                                                                      ##STR80##         H  F                                              n-C.sub.6 H.sub.13                                                                      ##STR81##         F  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR82##         H  H                                              CH.sub.2CHCH.sub.2                                                                      ##STR83##         H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR84##         F  F                                              n-C.sub.3 H.sub.7                                                                       ##STR85##         H  H                                              n-C.sub.3 H.sub.7                                                                       ##STR86##         H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR87##         F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR88##         F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR89##         H  H                                              n-C.sub.5 H.sub.11                                                                      ##STR90##         H  F                                              CH.sub.3 O                                                                              ##STR91##         F  F                                              CH.sub.3 O                                                                              ##STR92##         H  H                                              CH.sub.3 O                                                                              ##STR93##         H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR94##         H  H                                              CH.sub.2CHCH.sub.2                                                                      ##STR95##         H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR96##         F  F                                              C.sub.2 H.sub.5                                                                         ##STR97##         H  H                                              C.sub.2 H.sub.5                                                                         ##STR98##         H  F                                              C.sub.2 H.sub.5                                                                         ##STR99##         F  F                                              n-C.sub.3 H.sub.7                                                                       ##STR100##        H  H                                              n-C.sub.3 H.sub.7                                                                       ##STR101##        H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR102##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR103##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR104##        H  H                                              n-C.sub.5 H.sub.11                                                                      ##STR105##        H  F                                              CH.sub.3 O                                                                              ##STR106##        F  F                                              CH.sub.3 O                                                                              ##STR107##        H  H                                              CH.sub.3 O                                                                              ##STR108##        H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR109##        H  H                                              CH.sub.2CHCH.sub.2                                                                      ##STR110##        H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR111##        F  F                                              C.sub.2 H.sub.5                                                                         ##STR112##        H  H                                              C.sub.2 H.sub.5                                                                         ##STR113##        H  F                                              C.sub.2 H.sub.5                                                                         ##STR114##        F  F                                              n-C.sub.3 H.sub.7                                                                       ##STR115##        H  H                                              n-C.sub.3 H.sub.7                                                                       ##STR116##        H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR117##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR118##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR119##        H  H                                              n-C.sub.5 H.sub.11                                                                      ##STR120##        H  F                                              C.sub.2 H.sub.5                                                                         ##STR121##        H  H                                              C.sub.2 H.sub.5                                                                         ##STR122##        H  F                                              C.sub.2 H.sub.5                                                                         ##STR123##        F  F                                              n-C.sub.3 H.sub.7                                                                       ##STR124##        H  H                                              n-C.sub.3 H.sub.7                                                                       ##STR125##        H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR126##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR127##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR128##        H  H                                              n-C.sub.5 H.sub.11                                                                      ##STR129##        H  F                                              CH.sub.3 O                                                                              ##STR130##        F  F                                              CH.sub.3 O                                                                              ##STR131##        H  H                                              CH.sub.3 O                                                                              ##STR132##        H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR133##        H  H                                              CH.sub.2CHCH.sub.2                                                                      ##STR134##        H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR135##        F  F                                              C.sub.2 H.sub.5                                                                         ##STR136##        H  H                                              C.sub.2 H.sub.5                                                                         ##STR137##        H  F                                              C.sub.2 H.sub.5                                                                         ##STR138##        F  F                                              n-C.sub.3 H.sub.7                                                                       ##STR139##        H  H                                              n-C.sub.3 H.sub.7                                                                       ##STR140##        H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR141##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR142##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR143##        H  H                                              n-C.sub.5 H.sub.11                                                                      ##STR144##        H  F                                              CH.sub.3 O                                                                              ##STR145##        F  F                                              CH.sub.3 O                                                                              ##STR146##        H  H                                              CH.sub.3 O                                                                              ##STR147##        H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR148##        H  H                                              CH.sub.2CHCH.sub.2                                                                      ##STR149##        H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR150##        F  F                                              C.sub.2 H.sub.5                                                                         ##STR151##        H  H                                              C.sub.2 H.sub.5                                                                         ##STR152##        H  F                                              C.sub.2 H.sub.5                                                                         ##STR153##        F  F                                              n-C.sub.3 H.sub.7                                                                       ##STR154##        H  H                                              n-C.sub.3 H.sub.7                                                                       ##STR155##        H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR156##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR157##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR158##        H  H                                              n-C.sub.5 H.sub.11                                                                      ##STR159##        H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR160##        H  H                                              n-C.sub.3 H.sub.7                                                                       ##STR161##        H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR162##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR163##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR164##        H  H                                              n-C.sub.5 H.sub.11                                                                      ##STR165##        H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR166##        H  H                                              n-C.sub.3 H.sub.7                                                                       ##STR167##        H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR168##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR169##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR170##        H  H                                              n-C.sub.5 H.sub.11                                                                      ##STR171##        H  F                                              CH.sub.3 O                                                                              ##STR172##        F  F                                              CH.sub.3 O                                                                              ##STR173##        H  H                                              CH.sub.3 O                                                                              ##STR174##        H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR175##        H  H                                              CH.sub.2CHCH.sub.2                                                                      ##STR176##        H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR177##        F  F                                              C.sub.2 H.sub.5                                                                         ##STR178##        H  H                                              C.sub.2 H.sub.5                                                                         ##STR179##        H  F                                              C.sub.2 H.sub.5                                                                         ##STR180##        F  F                                              n-C.sub.3 H.sub.7                                                                       ##STR181##        H  H                                              n-C.sub.3 H.sub.7                                                                       ##STR182##        H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR183##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR184##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR185##        H  H                                              n-C.sub.5 H.sub.11                                                                      ##STR186##        H  F                                              CH.sub.3 O                                                                              ##STR187##        F  F                                              CH.sub.3 O                                                                              ##STR188##        H  H                                              CH.sub.3 O                                                                              ##STR189##        H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR190##        H  H                                              CH.sub.2CHCH.sub.2                                                                      ##STR191##        H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR192##        F  F                                              C.sub.2 H.sub.5                                                                         ##STR193##        H  H                                              C.sub.2 H.sub.5                                                                         ##STR194##        H  F                                              C.sub.2 H.sub.5                                                                         ##STR195##        F  F                                              n-C.sub.3 H.sub.7                                                                       ##STR196##        H  H                                              n-C.sub.3 H.sub.7                                                                       ##STR197##        H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR198##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR199##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR200##        H  H                                              n-C.sub.5 H.sub.11                                                                      ##STR201##        H  F                                              CH.sub.3 O                                                                              ##STR202##        F  F                                              CH.sub.3 O                                                                              ##STR203##        H  H                                              CH.sub.3 O                                                                              ##STR204##        H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR205##        H  H                                              CH.sub.2CHCH.sub.2                                                                      ##STR206##        H  F                                              CH.sub.2CHCH.sub.2                                                                      ##STR207##        F  F                                              n-C.sub.3 H.sub.7                                                                       ##STR208##        H  H                                              n-C.sub.3 H.sub.7                                                                       ##STR209##        H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR210##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR211##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR212##        H  H                                              n-C.sub.5 H.sub.11                                                                      ##STR213##        H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR214##        H  H                                              n-C.sub.3 H.sub.7                                                                       ##STR215##        H  F                                              n-C.sub.3 H.sub.7                                                                       ##STR216##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR217##        F  F                                              n-C.sub.5 H.sub.11                                                                      ##STR218##        H  H                                              n-C.sub.5 H.sub.11                                                                      ##STR219##        H  F                                              __________________________________________________________________________

EXAMPLE 2 ##STR220##

0.1 mol of trans-4-(trans-4-pentylcyclohexyl)cyclohexyl bromide, 0.05mol of zinc bromide and 0.2 mol of lithium granules in 150 ml oftoluene/THF (4:1) are treated with ultrasound at 15° C. for 3 hoursunder a nitrogen atmosphere. p-Bromo-1,1,3,3,3-pentafluoropropylbenzeneand 1.2 g of bis(diphenylphosphine)ferrocenepalladium(II) chloride areadded, and the mixture is stirred at room temperature for 72 hours.

100 ml of saturated ammonium chloride solution are added dropwise to thesolution, and the mixture is subsequently stirred for 15 minutes. Theorganic phase is separated off and subjected to customary work-up. C 55S_(M) (52) S_(G) 127 S_(B) 128 I

The following compounds of the formula ##STR221## are preparedanalogously:

    ______________________________________                                        R         (A.sup.1 Z.sup.1).sub.m A.sup.2 Z.sup.2                                                              L.sup.1                                                                             L.sup.2                                ______________________________________                                        C.sub.2 H.sub.5                                                                          ##STR222##            H     H                                      C.sub.2 H.sub.5                                                                          ##STR223##            H     F                                      C.sub.2 H.sub.5                                                                          ##STR224##            F     F                                      n-C.sub.3 H.sub.7                                                                        ##STR225##            H     H                                      n-C.sub.3 H.sub.7                                                                        ##STR226##            H     F                                      n-C.sub.3 H.sub.7                                                                        ##STR227##            F     F                                      n-C.sub.5 H.sub.11                                                                       ##STR228##            H     H                                      n-C.sub.5 H.sub.11                                                                       ##STR229##            H     F                                      n-C.sub.5 H.sub.11                                                                       ##STR230##            F     F                                      n-C.sub.6 H.sub.13                                                                       ##STR231##            H     H                                      n-C.sub.6 H.sub.13                                                                       ##STR232##            H     F                                      n-C.sub.6 H.sub.13                                                                       ##STR233##            F     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR234##            H     H                                      CH.sub.2 CHCH.sub.2                                                                      ##STR235##            H     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR236##            F     F                                      C.sub.2 H.sub.5                                                                          ##STR237##            H     H                                      C.sub.2 H.sub.5                                                                          ##STR238##            H     F                                      C.sub.2 H.sub.5                                                                          ##STR239##            F     F                                      n-C.sub.3 H.sub.7                                                                        ##STR240##            H     H                                      n-C.sub.3 H.sub.7                                                                        ##STR241##            H     F                                      n-C.sub.3 H.sub.7                                                                        ##STR242##            F     F                                      n-C.sub.5 H.sub.11                                                                       ##STR243##            H     F                                      n-C.sub.5 H.sub.11                                                                       ##STR244##            F     F                                      n-C.sub.6 H.sub.13                                                                       ##STR245##            H     H                                      n-C.sub.6 H.sub.13                                                                       ##STR246##            H     F                                      n-C.sub.6 H.sub.13                                                                       ##STR247##            F     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR248##            H     H                                      CH.sub.2 CHCH.sub.2                                                                      ##STR249##            H     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR250##            F     F                                      C.sub.2 H.sub.5                                                                          ##STR251##            H     H                                      C.sub.2 H.sub.5                                                                          ##STR252##            H     F                                      C.sub.2 H.sub.5                                                                          ##STR253##            F     F                                      n-C.sub.3 H.sub.7                                                                        ##STR254##            H     H                                      n-C.sub.3 H.sub.7                                                                        ##STR255##            H     F                                      n-C.sub.3 H.sub.7                                                                        ##STR256##            F     F                                      n-C.sub.5 H.sub.11                                                                       ##STR257##            H     H                                      n-C.sub.5 H.sub.11                                                                       ##STR258##            H     F                                      n-C.sub.5 H.sub.11                                                                       ##STR259##            F     F                                      n-C.sub.6 H.sub.13                                                                       ##STR260##            H     H                                      n-C.sub.6 H.sub.13                                                                       ##STR261##            H     F                                      n-C.sub.6 H.sub.13                                                                       ##STR262##            F     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR263##            H     H                                      CH.sub.2 CHCH.sub.2                                                                      ##STR264##            H     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR265##            F     F                                      C.sub.2 H.sub.5                                                                          ##STR266##            H     H                                      C.sub.2 H.sub.5                                                                          ##STR267##            H     F                                      C.sub.2 H.sub.5                                                                          ##STR268##            F     F                                      n-C.sub.3 H.sub.7                                                                        ##STR269##            H     H                                      n-C.sub.3 H.sub.7                                                                        ##STR270##            H     F                                      n-C.sub.3 H.sub.7                                                                        ##STR271##            F     F                                      n-C.sub.5 H.sub.11                                                                       ##STR272##            H     H                                      n-C.sub.5 H.sub.11                                                                       ##STR273##            H     F                                      n-C.sub.5 H.sub.11                                                                       ##STR274##            F     F                                      n-C.sub.6 H.sub.13                                                                       ##STR275##            H     H                                      n-C.sub.6 H.sub.13                                                                       ##STR276##            H     F                                      n-C.sub.6 H.sub.13                                                                       ##STR277##            F     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR278##            H     H                                      CH.sub.2 CHCH.sub.2                                                                      ##STR279##            H     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR280##            F     F                                      C.sub.2 H.sub.5                                                                          ##STR281##            H     H                                      C.sub.2 H.sub.5                                                                          ##STR282##            H     F                                      C.sub.2 H.sub.5                                                                          ##STR283##            F     F                                      n-C.sub.3 H.sub.7                                                                        ##STR284##            H     H                                      n-C.sub.3 H.sub.7                                                                        ##STR285##            H     F                                      n-C.sub.3 H.sub.7                                                                        ##STR286##            F     F                                      n-C.sub.5 H.sub.11                                                                       ##STR287##            H     H                                      n-C.sub.5 H.sub.11                                                                       ##STR288##            H     F                                      n-C.sub.5 H.sub.11                                                                       ##STR289##            F     F                                      n-C.sub.6 H.sub.13                                                                       ##STR290##            H     H                                      n-C.sub.6 H.sub.13                                                                       ##STR291##            H     F                                      n-C.sub.6 H.sub.13                                                                       ##STR292##            F     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR293##            H     H                                      CH.sub.2 CHCH.sub.2                                                                      ##STR294##            H     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR295##            F     F                                      C.sub.2 H.sub.5                                                                          ##STR296##            H     H                                      C.sub.2 H.sub.5                                                                          ##STR297##            H     F                                      C.sub.2 H.sub.5                                                                          ##STR298##            F     F                                      n-C.sub.3 H.sub.7                                                                        ##STR299##            H     H                                      n-C.sub.3 H.sub.7                                                                        ##STR300##            H     F                                      n-C.sub.3 H.sub.7                                                                        ##STR301##            F     F                                      n-C.sub.5 H.sub.11                                                                       ##STR302##            H     H                                      n-C.sub.5 H.sub.11                                                                       ##STR303##            H     F                                      n-C.sub.5 H.sub.11                                                                       ##STR304##            F     F                                      n-C.sub.6 H.sub.13                                                                       ##STR305##            H     H                                      n-C.sub.6 H.sub.13                                                                       ##STR306##            H     F                                      n-C.sub.6 H.sub.13                                                                       ##STR307##            F     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR308##            H     H                                      CH.sub.2 CHCH.sub.2                                                                      ##STR309##            H     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR310##            F     F                                      n-C.sub.3 H.sub.7                                                                        ##STR311##            H     H                                      n-C.sub.3 H.sub.7                                                                        ##STR312##            H     F                                      n-C.sub.3 H.sub.7                                                                        ##STR313##            F     F                                      n-C.sub.5 H.sub.11                                                                       ##STR314##            H     H                                      n-C.sub.5 H.sub.11                                                                       ##STR315##            H     F                                      n-C.sub.5 H.sub.11                                                                       ##STR316##            F     F                                      n-C.sub.6 H.sub.13                                                                       ##STR317##            H     H                                      n-C.sub.6 H.sub.13                                                                       ##STR318##            H     F                                      n-C.sub.6 H.sub.13                                                                       ##STR319##            F     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR320##            H     H                                      CH.sub.2 CHCH.sub.2                                                                      ##STR321##            H     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR322##            F     F                                      C.sub.2 H.sub.5                                                                          ##STR323##            H     H                                      C.sub.2 H.sub.5                                                                          ##STR324##            H     F                                      C.sub.2 H.sub.5                                                                          ##STR325##            F     F                                      n-C.sub.3 H.sub.7                                                                        ##STR326##            H     H                                      n-C.sub.3 H.sub.7                                                                        ##STR327##            H     F                                      n-C.sub.3 H.sub.7                                                                        ##STR328##            F     F                                      n-C.sub.5 H.sub.11                                                                       ##STR329##            H     H                                      n-C.sub.5 H.sub.11                                                                       ##STR330##            H     F                                      n-C.sub.5 H.sub.11                                                                       ##STR331##            F     F                                      n-C.sub.6 H.sub.13                                                                       ##STR332##            H     H                                      n-C.sub.6 H.sub.13                                                                       ##STR333##            H     F                                      n-C.sub.6 H.sub.13                                                                       ##STR334##            F     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR335##            H     H                                      CH.sub.2 CHCH.sub.2                                                                      ##STR336##            H     F                                      CH.sub.2 CHCH.sub.2                                                                      ##STR337##            F     F                                      n-C.sub.3 H.sub.7                                                                        ##STR338##            H     H                                      n-C.sub.3 H.sub.7                                                                        ##STR339##            H     F                                      n-C.sub.3 H.sub.7                                                                        ##STR340##            F     F                                      n-C.sub.5 H.sub.11                                                                       ##STR341##            H     H                                      n-C.sub.5 H.sub.11                                                                       ##STR342##            H     F                                      n-C.sub.5 H.sub.11                                                                       ##STR343##            F     F                                      n-C.sub.3 H.sub.7                                                                        ##STR344##            H     H                                      n-C.sub.3 H.sub.7                                                                        ##STR345##            H     F                                      n-C.sub.3 H.sub.7                                                                        ##STR346##            F     F                                      n-C.sub.5 H.sub.11                                                                       ##STR347##            H     H                                      n-C.sub.5 H.sub.11                                                                       ##STR348##            H     F                                      n-C.sub.5 H.sub.11                                                                       ##STR349##            F     F                                      ______________________________________                                    

MIXTURE EXAMPLES

    ______________________________________                                        Example A                                                                     PCH-5F     9.0%      Clearing point [°C.]:                                                                91.4                                       PCH-6F     7.2%      Δn [589 nm, 20° C.]:                                                           0.1001                                     PCH-7F     5.4%      Δε [1 kHz, 20° C.]:                                                    5.78                                       CCP-2OCF.sub.3                                                                           7.2%      ν [mm.sup.2, s.sup.-1 ]:                                                                 16.10                                      CCP-3OCF.sub.3                                                                           10.8%                                                              CCP-4OCF.sub.3                                                                           8.1%                                                               CCP-5OCF.sub.3                                                                           8.1%                                                               BCH-3F.F   10.8%                                                              BCH-5F.F   9.0%                                                               ECCP-3OCF.sub.3                                                                          4.5%                                                               ECCP-5OCF.sub.3                                                                          4.5%                                                               CBC-33F    1.8%                                                               CBC-53F    1.8%                                                               CBC-55F    1.8%                                                               CPP-5-D1T  10.0%                                                              Example B                                                                     PCH-5F     9.0%      Clearing point [°C.]:                                                                93                                         PCH-6F     7.2%      Δn [589 nm, 20° C.]:                                                           0.0949                                     PCH-7F     5.4%      Δε [1 kHz, 20° C.]:                                                    5.57                                       CCP-2OCF.sub.3                                                                           7.2%      ν [mm.sup.2, s.sup.-1 ]:                                                                 16.10                                      CCP-3OCF.sub.3                                                                           10.8%                                                              CCP-4OCF.sub.3                                                                           8.1%                                                               CCP-5OCF.sub.3                                                                           8.1%                                                               BCH-3F.F   10.8%                                                              BCH-5F.F   9.0%                                                               ECCP-3OCF.sub.3                                                                          4.5%                                                               ECCP-5OCF.sub.3                                                                          4.5%                                                               CBC-33F    1.8%                                                               CBC-53F    1.8%                                                               CBC-55F    1.8%                                                               CCP-5-D1T  10.0%                                                              ______________________________________                                    

We claim:
 1. A partially fluorinated benzene compound of formula I##STR350## wherein R is H, alkyl having 1 to 15 carbon atoms which isunsubstituted, monosubstituted by CN or CF₃ or at least monosubstitutedby halogen, wherein one or more CH₂ groups can be replaced, in each caseindependently of one another by --O--, --S--, ##STR351## --CO--,--CO--O--, --O--CO-- or --O--CO--O--, without O atoms being linkeddirectly to one another, or alkenyl having 1 to 15 carbon atoms which isunsubstituted, monosubstituted by CN or CF₃ or at least monosubstitutedby halogen, wherein one or more CH₂ groups can be replaced, in each caseindependently of one another, by --O--, --S--, ##STR352## --CO--,--CO--O--, --O--CO-- or --O--CO--O--, without O atoms being linkeddirectly to one another;A¹ and A² are each, independently of oneanother,(a) trans-1,4-cyclohexylene radical in which one or morenonadjacent CH₂ groups can each be replaced by --O-- or --S--, (b)1,4-phenylene in which one or two CH groups can be replaced by N, (c)1,4-cyclohexenylene, 1,4-bicyclo-(2,2,2)octylene, piperidine-1,4-diyl,naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl or1,2,3,4-tetrahydronaphthalene-2,6-diyl, wherein radicals of (a) and (b)can be substituted by one or two fluorine atoms; Z¹ and Z² are each,independently of one another, --CO--O--, --O--CO--, --CH₂ O--, --CH₂ CH₂--, --CH═CH--, --C≡C-- or a single bond, and one of Z¹ and Z² can alsobe --(CH₂)₄ -- or --CH═CH--CH₂ CH₂ --; m is 0, 1 or 2; and L¹ and L² areeach, independently of one another, H or F.
 2. A compound according toclaim 1, wherein said compound is of the formula ##STR353## in which R,L¹ and L² are as defined.
 3. A compound according to claim 1, whereinsaid compound is of the formula ##STR354## in which R, L¹ and L² are asdefined.
 4. A compound according to claim 1, wherein said compound is ofthe formula I6 ##STR355## in which R is as defined.
 5. A compoundaccording to claim 1, wherein said compound is of the formula I7##STR356## in which R is as defined.
 6. A compound according to claim 1,wherein said compound is of the formula I9 ##STR357## in which R is asdefined.
 7. In a liquid-crystalline medium having at least twoliquid-crystalline compounds, the improvement wherein said mediumcontains at least one compound according to claim
 1. 8. In aliquid-crystal display element containing a liquid-crystalline medium,the improvement wherein said display element contains a medium accordingto claim
 7. 9. In an electrooptical display using a liquid-crystaldisplay element, the improvement wherein said display element contains,as a dielectric, a liquid-crystalline medium according to claim
 7. 10. Acompound according to claim 1, wherein one of Z¹ and Z² is --(CH₂)₄ --or --CH═CH--CH₂ CH₂ -- and the other is a single bond.
 11. A compoundaccording to claim 1, wherein L¹ and L² are each H.
 12. A compoundaccording to claim 1, wherein L¹ is F and L² is H.
 13. A compoundaccording to claim 1, wherein L¹ and L² are each F.
 14. A compoundaccording to claim 1, wherein said compound is of the formula I12##STR358## in which R is as defined.
 15. A compound according to claim1, wherein said compound is of the formula I25 ##STR359## in which R isas defined.
 16. A liquid-crystalline medium according to claim 7,wherein said medium contains 1-40 wt. % of compounds of formula I.
 17. Aliquid-crystalline medium according to claim 7, wherein said mediumcontains 45-90 wt. % of compounds of formula I.
 18. A compound accordingto claim 1, whereinA¹ and A² are each independently 1,4-cyclohexylenewhich is unsubstituted or mono- or disubstituted by F or CN,1,4-cyclohexenylene, 1,4-phenylene which is unsubstituted or mono- ordisubstituted by F or CN, pyrimidine-2,5-diyl, pyridine-2,5-diyl or1,3-dioxane-2,5-diyl; Z¹ and Z² are each independently a single bond,--CO--O--, --O--CO-- or --CH₂ CH₂ --; and R is methyl, ethyl, propyl,butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, tridecyl, tetradecyl,pentadecyl, methoxy, ethoxy, propoxy, butoxy, pentoxy, heptoxy, octoxy,nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy, tetradecoxy, vinyl,prop-1-enyl, prop-2-enyl, but-1-enyl, but-2-enyl, but-3-enyl,pent-1-enyl, pent-2-enyl, pent-3-enyl, pent-4-enyl, hex-1-enyl,hex-2-enyl, hex-3-enyl, hex-4-enyl, hex-5-enyl, hept-1-enyl,hept-2-enyl, hept-3-enyl, hept-4-enyl, hept-5-enyl, hept-6-enyl,oct-1-enyl, oct-2-enyl, oct-3-enyl, oct-4-enyl, oct-5-enyl, oct-6-enyl,oct-7-enyl, non-1-enyl, non-2-enyl, non-3-enyl, non-4-enyl, non-5-enyl,non-6-enyl, non-7-enyl, non-8-enyl, dec-1-enyl, dec-2-enyl, dec-3-enyl,dec-4-enyl, dec-5-enyl, dec-6-enyl, dec-7-enyl, dec-8-enyl ordec-9-enyl.